// ----------------------------------------------------------------------
 // <summary>
 // 限制只能输入数字
 // </summary>
 // ----------------------------------------------------------------------
 $.fn.onlyNum = function () {
   $(this).keypress(function (event) {
     var eventObj = event || e;
     var keyCode = eventObj.keyCode || eventObj.which;
     if ((keyCode >= && keyCode <= ))
       return true;
     else
       return false;
   }).focus(function () {
   //禁用输入法
     this.style.imeMode = 'disabled';
   }).bind("paste", function () {
   //获取剪切板的内容
     var clipboard = window.clipboardData.getData("Text");
     if (/^\d+$/.test(clipboard))
       return true;
     else
       return false;
   });
 }; 

// ----------------------------------------------------------------------
 // <summary>
 // 限制只能输入字母
 // </summary>
 // ----------------------------------------------------------------------
 $.fn.onlyAlpha = function () {
   $(this).keypress(function (event) {
     var eventObj = event || e;
     var keyCode = eventObj.keyCode || eventObj.which;
     if ((keyCode >= && keyCode <= ) || (keyCode >= && keyCode <= ))
       return true;
     else
       return false;
   }).focus(function () {
     this.style.imeMode = 'disabled';
   }).bind("paste", function () {
     var clipboard = window.clipboardData.getData("Text");
     if (/^[a-zA-Z]+$/.test(clipboard))
       return true;
     else
       return false;
   });
 }; 

 // ----------------------------------------------------------------------
 // <summary>
 // 限制只能输入数字和字母
 // </summary>
 // ----------------------------------------------------------------------
 $.fn.onlyNumAlpha = function () {
   $(this).keypress(function (event) {
     var eventObj = event || e;
     var keyCode = eventObj.keyCode || eventObj.which;
     if ((keyCode >= && keyCode <= ) || (keyCode >= && keyCode <= ) || (keyCode >= && keyCode <= ))
       return true;
     else
       return false;
   }).focus(function () {
     this.style.imeMode = 'disabled';
   }).bind("paste", function () {
     var clipboard = window.clipboardData.getData("Text");
     if (/^(\d|[a-zA-Z])+$/.test(clipboard))
       return true;
     else
       return false;
   });
 }; 

 $(function () {
   // 限制使用了onlyNum类样式的控件只能输入数字
   $(".onlyNum").onlyNum();
   //限制使用了onlyAlpha类样式的控件只能输入字母
   $(".onlyAlpha").onlyAlpha();
   // 限制使用了onlyNumAlpha类样式的控件只能输入数字和字母
   $(".onlyNumAlpha").onlyNumAlpha();
  });

 <ul>
     <li>只能输入数字：<input type="text" class="onlyNum" /></li>
     <li>只能输入字母：<input type="text" class="onlyAlpha" /></li>
     <li>只能输入数字和字母：<input type="text" class="onlyNumAlpha" /></li>
 </ul>